The knot (pronounced not) is a unit of speed equal to one nautical mile (1.852 km) per hour, approximately 1.151 mph. The abbreviation kn is preferred by the International Hydrographic Organization (IHO), which includes every major sea-faring nation; however, the abbreviations kt (singular) and kts (plural) are also widely used. However, use of the abbreviation kt for knot conflicts with the SI symbol for kilotonne. The knot is a non-SI unit accepted for use with the International System of Units (SI). Worldwide, the knot is used in meteorology, and in maritime and air navigation—for example, a vessel travelling at 1 knot along a meridian travels one minute of geographic latitude in one hour. Etymologically, the term knot derives from counting the number of knots in the line that unspooled from the reel of a chip log in a specific time.

1,852 m is the length of the internationally-agreed nautical mile. The US adopted the international definition in 1954, having previously used the US nautical mile (1,853.248 m). The UK adopted the international nautical mile definition in 1970, having previously used the UK Admiralty nautical mile (6,080 ft [1,853.184 m]).

A knot is a method of fastening or securing linear material such as rope by tying or interweaving. It may consist of a length of one or several segments of rope, string, webbing, twine, strap, or even chain interwoven such that the line can bind to itself or to some other object—the "load". Knots have been the subject of interest for their ancient origins, their common uses, and the area of mathematics known as knot theory.

There is a large variety of knots, each with properties that make it suitable for a range of tasks. Some knots are used to attach the rope (or other knotting material) to other objects such as another rope, cleat, ring, or stake. Some knots are used to bind or constrict objects. Decorative knots usually bind to themselves to produce attractive patterns.

While some people can look at diagrams or photos and tie the illustrated knots, others learn best by watching how a knot is tied. Knot tying skills are often transmitted by sailors, scouts, climbers, cavers, arborists, rescue professionals, fishermen, linemen and surgeons.